Cracked Carb - Repaired

Fri Jun 15, 2012 12:49 pm

I decided to paint the hood, gas tank, and grille on my Super A. I removed the parts and was putting on a pony tank and had to remove the elbow from the carb and install a barb fitting for the pony tank hose. I didn't have too many turns on the barb when I heard a "Tink". I knew exactly what it was . Now I have a hairline crack about 1/4 inch long on the top of the fitting hole. The carb is cast iron. Is there a fix for this aside from a new carb?

Thanks, Tom

Last edited by twotone on Tue Jun 26, 2012 1:25 pm, edited 1 time in total.

Re: Cracked Carb

Sun Jun 17, 2012 7:58 pm

I would think that if you take it apart, someone who is good with a torch could braze it.

Re: Cracked Carb

Sun Jun 17, 2012 8:43 pm

I'm not sure about an "A", but the carb inlet threads on a Cub are 1/2-20. A lot of your barbed fittings look similar but they are i1/8 npt which are a bit bigger. They will strip the threads on a cub carb and more than likely crack the inlet on a cast carb. Make sure which thread size you have before trying again.

Re: Cracked Carb

Mon Jun 18, 2012 7:36 am

I was thinking some JB Weld might work since it is a non pressurized system.

Tom

Re: Cracked Carb

Mon Jun 18, 2012 8:07 am

Tom:

Is it a Carter UT carb?

Re: Cracked Carb

Mon Jun 18, 2012 11:50 am

It is a Carter carb, but the book just gives a part number. The elbow fitting I took out I replaced it with the same thread gas valve and barb fitting. I think I might have put too much pipe tape and screwed it too far.

Tom

Re: Cracked Carb

Mon Jun 18, 2012 12:14 pm

How about silver solder?

Re: Cracked Carb

Mon Jun 18, 2012 12:38 pm

I don't know Don, It's a tiny ultra-hairline crack on top of the threaded portion of the inlet. I could get a new carb top, or try and fix what I have. I was hoping more people were on board with my JB Weld idea, but if it's not the right way, I won't do it. Yes, I'm looking for the easiest way out.

Tom

Re: Cracked Carb

Mon Jun 18, 2012 1:20 pm

Tom:

Easiest way out aside from buying a new replacement carb is having the Carter brazed or silver soldered. And competent welding shop/machine shop should be able to do it for a minimum charge ... that is the route I would explore first.

Re: Cracked Carb

Mon Jun 18, 2012 1:37 pm

Tom, I think the JB Weld would work, except I think you'd want to find a brass fitting/bushing that could be left in place so the crack line wouldn't tend to have opening pressure on it whenever you removed/tightened the fitting. I think you'd also need to open up the crack so that there would be some surface area for the JB to adhere to. Drilling a small hole part way through at the end of the crack may help to keep it from spreading any further.

Bob

Re: Cracked Carb

Mon Jun 18, 2012 1:47 pm

I just removed the fitting and it has the exact threads as the original elbow that was in there. When I remove the fitting, the crack disappears. If I put in the original fitting with no thread tape, I can thread it all the way in with my fingers and the crack doesn't appear. I'm going to have put something on the threads when I put it all together though. Maybe some Indian Head Varnish on the threads. That should put a couple of people in my corner!

Re: Cracked Carb

Mon Jun 18, 2012 2:19 pm

Tom, Is the fitting straight threads like the Cub (1/2-20), or is it pipe thread, and if so, what size?

Bob

Re: Cracked Carb

Mon Jun 18, 2012 2:32 pm

Using my plastic thread guide, 3/8 is too small, 7/16 is too big. It fits perfect in a Metric #10. Both fittings have the same threads.It doesn't appear to be pipe thread, I can put both fittings in all the way by hand with no thread tape on them.

Re: Cracked Carb

Mon Jun 18, 2012 3:43 pm

Tom,

I have something for you to try. When you are ready to reassemble the fuel system and run the tractor, install the elbow as normal. Do not use teflon tape or any other sealer prior to assembly. Clean the threads and crack well with carb cleaner. After assembly, but prior to introducing fuel, apply some Permatex green threadlocker to the threads and the crack. Allow it to cure according to the label.

The threadlocker is gasoline resistant and should seal everything properly. The good news is this solution is not permanent and will not further impact the carb. You can still JB weld or solder the crack if this doesn't hold. And it's not expensive.

Re: Cracked Carb

Mon Jun 18, 2012 4:08 pm

Sounds like a plan Don. I really don't think this is going to be as serious of a problem as I first thought. (A Man Has To Have Dreams) I'll give the green thread locker a try during assembly. Thanks for your help.